Bug #7878 with utf_general_ci, equals (=) has problem with accent insensitivity

Backporting Monty's fix for 5.0 into 4.1.

include/my_base.h

@@ -340,6 +340,7 @@ enum ha_base_keytype {
 #define HA_STATE_BUFF_SAVED	512	/* If current keybuff is info->buff */
 #define HA_STATE_ROW_CHANGED	1024	/* To invalide ROW cache */
 #define HA_STATE_EXTEND_BLOCK	2048
+#define HA_STATE_RNEXT_SAME	4096	/* rnext_same was called */
 
 enum en_fieldtype {
   FIELD_LAST=-1,FIELD_NORMAL,FIELD_SKIP_ENDSPACE,FIELD_SKIP_PRESPACE,

myisam/mi_rnext_same.c

@@ -57,7 +57,11 @@ int mi_rnext_same(MI_INFO *info, byte *buf)
 #endif
     case HA_KEY_ALG_BTREE:
     default:
-      memcpy(info->lastkey2,info->lastkey,info->last_rkey_length);
+      if (!(info->update & HA_STATE_RNEXT_SAME))
+      {
+        /* First rnext_same; Store old key */
+        memcpy(info->lastkey2,info->lastkey,info->last_rkey_length);
+      }
       for (;;)
       {
         if ((error=_mi_search_next(info,keyinfo,info->lastkey,
@@ -81,7 +85,7 @@ int mi_rnext_same(MI_INFO *info, byte *buf)
     rw_unlock(&info->s->key_root_lock[inx]);
 	/* Don't clear if database-changed */
   info->update&= (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED);
-  info->update|= HA_STATE_NEXT_FOUND;
+  info->update|= HA_STATE_NEXT_FOUND | HA_STATE_RNEXT_SAME;
 
   if (error)
   {

mysql-test/r/ctype_latin1_de.result

@@ -326,3 +326,15 @@ latin1_german2_ci	6109
 latin1_german2_ci	61
 latin1_german2_ci	6120
 drop table t1;
+SET NAMES latin1;
+CREATE TABLE t1 (
+col1 varchar(255) NOT NULL default ''
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 collate latin1_german2_ci;
+INSERT INTO t1 VALUES (''),('ss'),('ss');
+ALTER TABLE t1 ADD KEY ifword(col1);
+SELECT * FROM t1 WHERE col1='' ORDER BY col1, BINARY col1;
+col1
+ss
+ss
+
+DROP TABLE t1;

mysql-test/t/ctype_latin1_de.test

@@ -116,3 +116,19 @@ SELECT FIELD('ue',s1), FIELD('
 DROP TABLE t1;
 
 -- source include/ctype_filesort.inc
+
+#
+# Bug#7878 with utf8_general_ci, equals (=) has problem with
+# accent insensitivity.
+# Although originally this problem was found with UTF8 character set,
+# '=' behaved wrong for latin1_german2_ci as well.
+# Let's check it does not work incorrect anymore.
+# 
+SET NAMES latin1;
+CREATE TABLE t1 (
+  col1 varchar(255) NOT NULL default ''
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 collate latin1_german2_ci;
+INSERT INTO t1 VALUES (''),('ss'),('ss');
+ALTER TABLE t1 ADD KEY ifword(col1);
+SELECT * FROM t1 WHERE col1='' ORDER BY col1, BINARY col1;
+DROP TABLE t1;